DIAULAX. 7 



before backwards, very slightly so from side to side ; the regions very indistinctly marked, 

 the protogastric lobes with a small, almost obsolete tubercle, the posterior median portion 

 of the gastric and the cardiac region slightly raised. There are two parallel, shallow 

 furrows extending nearly straight across the carapace ; the boundary line of the anterior 

 one, the nuchal furrrow, forming a distinctly marked edge ; the posterior furrow is in 

 some specimens almost obsolete. At the lateral margins the sides of the carapace form a 

 sharp angle with the upper surface ; there is a small tubercle on the lateral margin 

 immediately in front of the nuchal furrow, and a rather larger one behind it- the latero- 

 anterior margin is somewhat curved, the latero-posterior nearly straight. The front is 

 simple, somewhat incurved, depressed in the centre ; the orbits oval, transverse, distant, 

 being separated by a wide antennary fossa, which is open to the orbit. The upper margin 

 of the orbit is entire ; in the lower margin is a rather broad groove. The epistome is 

 pentagonal, and the angles are much produced. The claw, of which only a fragment has 

 been found, is extremely large in proportion, is robust and quite smooth ; the hand round 

 and gibbous, and as broad as it is long ; the moveable finger carinated above. Of the 

 ambulatory legs nothing remains but the basal portions, and from these it appears that 

 the last pair are placed on a much higher level than the others. There are no remains in 

 any of the specimens I have seen of footjaws, antennas, or abdomen. 



Length of carapace, 09 inch; breadth, 07 inch. 



Found in the upper Greensand of Cambridge, from which there are specimens in Mr. 

 Carter's collection and in my own. 



Obs. The extremely imperfect state of all the specimens hitherto found of this species 

 has deterred me from attempting to offer any formal generic character, and the same 

 circumstance renders it very doubtful to what group of recent Crustacea it is most nearly 

 allied. Mr. Carter has suggested to me its probable affinity to the Thelphusadae, and, 

 certainly, the general form of the carapace, the wide oval orbit, and the robust claw, 

 would seem to sanction this opinion ; but in the absence of all those organs by which the 

 essential relations of a group are indicated, I can scarcely admit into a family, of which 

 all the known species inhabit the banks of rivers in the interior of the countries where 

 they are found, a species so entirely confined to a bed of strictly marine origin. I have, 

 therefore, assigned to it a provisional place amongst the Canceridae, without attempting, 

 with our limited means of forming a judgment, to decide upon its more intimate relations. 

 It is one of the rarest forms in the prolific bed of the Cambridge upper Greensand, there 

 being but few specimens even in Mr. Carter's fine collection of fossil Crustaceans front 

 this locality. I have dedicated it to that gentleman, to whom I am indebted for first 

 bringing it to my notice, and for the loan of the specimens from which my description 

 and figures are derived. 



